In a scanning electron microscope, an object to be observed is usually rested on a sample mount. Then, the sample mount is moved by a sample stage driven by a stepping motor, a piezoelectric element, or the like. Patent Document 1, for example, discloses an invention made for accurately moving a visual field even when a stage has a backlash or a feed screw has a pitch error.
A prior-art scanning electron microscope (SEM) is shown in FIG. 1, details of a sample-moving stage thereof in FIG. 1 are shown in FIG. 2, a cross-sectional view taken along line A-A in FIG. 2 is shown in FIG. 3, and an external view from a direction of arrows, taken along line B-B in FIG. 2, is shown in FIG. 4. The scanning electron microscope, used to observe a shape of a sample surface, irradiates, through condenser lenses 2 and an objective lens 3, the surface of the sample 6 mounted on the sample-moving stage 5 inside a sample chamber 4, while scanning this sample surface with an electron beam generated by an electron gun 1, and then uses a secondary-electron detector 7 to capture a secondary electron originating from the sample. Reference numbers 9 to 13 in FIG. 1 denote vacuum pumps that create a vacuum in the sample chamber 4, an electron gun chamber 8, and the like. A stage casing 14 is installed on a side of the sample chamber 4, and a z-table 15 is coupled to the stage casing 14 via cross roller bearings 16a and 16b. The z-table 15 is pulled upward by a spring 17, then guided along cross roller guides 16a and 16b, and driven by rotation of a z-stepping motor 18. This makes a male screw of a z-moving shaft 19 and a female screw 64 mounted on the z-table 15, properly act to move the z-table 15 and thus to move the sample 6 in a z-direction. A tilting shaft 21 is mounted at one end of a tilting table 20, and the tilting shaft 21 is pivotally coupled to the z-table 15 via roller bearings 22 and 23. A locking plate 24 is mounted at the other end of the tilting table 20 and pushed by a stage-locking mechanism 25 mounted in the sample chamber 4.
A worm wheel 26a is fitted at an end of the tilting shaft 21, and a worm gear 26b formed to be combined with the worm wheel 26a is supported by ball bearings 27 and 28 and connected to the z-table 15 via bearing housings 29 and 30. The worm wheel 26a and a T-stepping motor 31 that rotates the worm gear 26b are coupled to each other by spline shafts 32a and 32b so as to be able to follow a movement of the z-moving member 15 in the z-direction. Rotation of the T-stepping motor 31 rotates the tilting shaft 21, thus tilts the sample 6, and retains the sample 6 at a fixed tilt angle. An x-table 33 that moves the sample 6 in an x-direction is mounted on the tilting table 20 via a cross roller guide 34. The x-table 33 is driven by a feed action of an x-ball screw 35 and an x-ball screw nut 36. The x-ball screw nut 36 is fixed to the x-table 33. The x-ball screw 35 is supported at both ends thereof by ball bearings 37 and 38, and is connected to the tilting table 20 at bearing housings 39 and 40. The x-ball screw 35 and an x-stepping motor 41 that rotates the x-ball screw 35 are coupled to each other by an x-stage joint 42. The x-stage joint 42 includes one pair of joint portions, 42a and 42b, for angle follow-up, and a telescopic portion 42c for length control with a ball spline.
The x-table 33 drives the x-stepping motor 41 to rotate the x-ball screw 35 via the x-stage joint 42 and feed the x-ball screw nut 36. This feed action moves the x-table 33 in the x-direction, hence moving the sample in the x=direction. A y-table 43 is mounted on the x-table 33 via cross roller guides 44a and 44b. The y-table 43 is driven by a feed action of a y-ball female screw 45 and a y-ball screw nut 46. The y-ball screw nut 46 is fixed to the y-table 43. The y-ball screw 45 is supported at both ends thereof by ball bearings 47 and 48, and is connected to the x-table 33 at bearing housings 49 and 50. A bevel gear 51a is fitted at one end of the y-ball screw 46, and a bevel gear 51b that meshes with the bevel gear 51a is supported by a ball bearing (not shown) and fixed at a bearing housing 53 to the x-table. The bevel gear 51b is coupled to a y-stepping motor 54 that rotates the y-ball screw 45, by a y-stage joint 55.
The y-stage joint 55 includes one pair of joint portions, 55a and 55b, for angle follow-up, and a telescopic portion 55c for length control with a ball spline. The y-table 43 drives the stepping motor 54 to rotate the bevel gears 51a, 51b and the y-ball screw 45 via the y-stage joint 55 and feed the y-ball screw nut 46. This feed action moves the y-table 43 in a y-direction, hence moving the sample in the y-direction. A rotation table 56 has a worm wheel 57a and is pivotally coupled to the y-table 43 by a ball bearing 58. A worm gear 57b is supported at both ends thereof by ball bearings 59 and 60, and is connected to the y-table 43 at bearing housings 61 and 62.
The worm gear 57b is rotated by a DC motor 63. Rotation of the DC motor 63 turns the worm gear 57b and the worm wheel 57a, thus rotating the rotation table 56 and hence the sample. The sample 6 is mounted in bonded form on a sample holder 65, and the sample holder 65 is inserted in and fixed to a holder stage 66 mounted on the rotation table 56. In this form, the sample is fed in the x-, y-, z-directions, rotated, and tilted.